The use of tunnel driers to dry wet material is well known. In a tunnel drier of a known design, a moving drier tray transports wet material through the drier tunnel. Heated air is typically used as a heat source to dry the wet material. After the material exits from the drier tunnel, it is removed from the drier tray as dry product. Tunnel driers with more than one drier tray are also known to those familiar with the art.
One problem with tunnel driers is that there is a tendency for small amounts of dry product to adhere to the drier tray and hence repeatedly cycle through the drier tunnel. This is undesirable because overdried product may become degraded due to excessive heat exposure. For example, one well known use of tunnel driers is to dry synthetic rubber. Small amounts of synthetic rubber sometimes adhere to the drier tray and eventually may become discoloured due to excessive heat exposure. If the discoloured synthetic rubber subsequently breaks loose from the drier tray and mixes with wet product passing through the drier, visible contamination of the dry finished product by the discoloured material results. It is therefore necessary to periodically clean the drier tray to remove accumulations of material that have adhered to it in order to produce a dry finished product of consistently high quality.
One method of cleaning the drier tray is to wash it with water under high pressure. This is typically done by a workman who manually positions a high pressure water nozzle in front of the tray, thus directing a flow of high pressure water to remove the accumulation of adhered material. The pressure of the water should be high enough to efficiently remove the adhered material but it should be low enough to avoid damaging the drier tray. A water pressure of 250-400 atmospheres has been found to be suitable for this process. The drier tray is in motion when it is being cleaned, to allow the workman to clean the tray as it rotates past him. Thus, the workman washes the entire width of the drier tray as it rotates past him.
The workman is unable to immediately view the result of his work due to the effect of water splashing off the drier tray. This is a problem because the workman might miss cleaning a part of the drier tray and not notice it as it rotates past him. As previously noted, the quality of the product being dried can be adversely affected by the material that adheres to the drier tray and, thus, proper cleaning of the tray is important. In addition, the cleaning process is labour intensive and expensive.